1. Field of the Invention
The present invention relates generally to bridge and fracture plugs used in oil and gas wells.
2. Related Art
Just prior to beginning “production,” oil and gas wells are completed using a complex process involving explosive charges and high pressure fluids. Once drilling is complete, a well is lined with steel pipe backed with cement that bridges the gap between the pipe outer diameter and rock face. The steel/cement barrier is then perforated with explosive shaped charges. High pressure fluids are then pumped down the well, through the perforations and into the rock formation to prepare the rock and well for the flow of gas and oil into the casing and up the well. Depending on numerous factors including the depth of the well, size and active “levels” in the reservoir, reservoir pressure, etc. this fracturing process is repeated several times in a given well—from a few elevations to as many as 30. As they prepare to “Frac” at each level, well technicians set a temporary plug in the bore of the steel casing pipe (just below where they will perforate) that will then allow them to pump “Frac fluids” and sand down through the perforations and into the reservoir. Use of the temporary plug prevents contaminating the already-fractured levels below. This process is repeated several times, as the Frac operation moves up the well, until all desired zones have been stimulated. At each level, the temporary plugs are usually left in place, so that they can all be drilled out at the end of the process, in a single operation.
To reduce the time needed to complete each well, is advantageous to use temporary plugs constructed primarily from soft metal alloys and composite materials (fiberglass and high performance plastics) that can be drilled out quickly, but still withstand the required pressures (up to 10,000 psi either upward or downward) and temperatures (up to 350° F.) for a period up to several weeks, in what is a very hostile environment.
One disadvantage with some prior plugs is that they must be shipped from the factory in the configuration in which they will be used in the well. For example, a frac plug allows upward flow but blocks downward flow. A bridge plug blocks flow in both directions. A soluble insert plug will temporary block flow in both directions and then reconfigure itself to allow flow in one direction. Thus, different types of plugs must be shipped to the well. Unfortunately, the well operator does not often know which plugs he wants installed at each level until he evaluates the well's response to the frac operations. Therefore, the tool hand (usually the plug supplier) and operator are unable to anticipate which mix of frac and bridge plugs will be needed with each well. This situation also creates a risk for both parties of having too many or too few of one kind or other plug causing project delays, stranded inventory and cash flow problems.